Quantification of Byproduct Formation from Portable Air Cleaners Using a Proposed Standard Test Method.

In response to the COVID-19 pandemic, air cleaning technologies were promoted as useful tools for disinfecting public spaces and combating airborne pathogen transmission. However, no standard method exists to assess the potentially harmful byproduct formation from air cleaners. Through a consensus standard development process, a draft standard test method to assess portable air cleaner performance was developed, and a suite of air cleaners employing seven different technologies was tested. The test method quantifies not only the removal efficiency of a challenge chemical suite and ultrafine particulate matter but also byproduct formation. Clean air delivery rates (CADRs) are used to quantify the chemical and particle removal efficiencies, and an emission rate framework is used to quantify the formation of formaldehyde, ozone, and other volatile organic compounds. We find that the tested photocatalytic oxidation and germicidal ultraviolet light (GUV) technologies produced the highest levels of aldehyde byproducts having emission rates of 202 and 243 µg h-1, respectively. Additionally, GUV using two different wavelengths, 222 and 254 nm, both produced ultrafine particulate matter.

Ventilation in a Residential Building Brings Outdoor NOx Indoors with Limited Implications for VOC Oxidation from NO3 Radicals.

Energy-efficient residential building standards require the use of mechanical ventilation systems that replace indoor air with outdoor air. Transient outdoor pollution events can be transported indoors via the mechanical ventilation system and other outdoor air entry pathways and impact indoor air chemistry. In the spring of 2022, we observed elevated levels of NOx (NO + NO2) that originated outdoors, entering the National Institute of Standards and Technology (NIST) Net-Zero Energy Residential Test Facility through the mechanical ventilation system. Using measurements of NOx, ozone (O3), and volatile organic compounds (VOCs), we modeled the effect of the outdoor-to-indoor ventilation of NOx pollution on the production of nitrate radical (NO3), a potentially important indoor oxidant. We evaluated how VOC oxidation chemistry was affected by NO3 during NOx pollution events compared to background conditions. We found that nitric oxide (NO) pollution introduced indoors titrated O3 and inhibited the modeled production of NO3. NO ventilated indoors also likely ceased most gas-phase VOC oxidation chemistry during plume events. Only through the artificial introduction of O3 to the ventilation duct during a NOx pollution event (i.e., when O3 and NO2 concentrations were high relative to typical conditions) were we able to measure NO3-initiated VOC oxidation products, indicating that NO3 was impacting VOC oxidation chemistry.

Assessing Human Exposure to SVOCs in Materials, Products, and Articles: A Modular Mechanistic Framework.

A critical review of the current state of knowledge of chemical emissions from indoor sources, partitioning among indoor compartments, and the ensuing indoor exposure leads to a proposal for a modular mechanistic framework for predicting human exposure to semivolatile organic compounds (SVOCs). Mechanistically consistent source emission categories include solid, soft, frequent contact, applied, sprayed, and high temperature sources. Environmental compartments are the gas phase, airborne particles, settled dust, indoor surfaces, and clothing. Identified research needs are the development of dynamic emission models for several of the source emission categories and of estimation strategies for critical model parameters. The modular structure of the framework facilitates subsequent inclusion of new knowledge, other chemical classes of indoor pollutants, and additional mechanistic processes relevant to human exposure indoors. The framework may serve as the foundation for developing an open-source community model to better support collaborative research and improve access for application by stakeholders. Combining exposure estimates derived using this framework with toxicity data for different end points and toxicokinetic mechanisms will accelerate chemical risk prioritization, advance effective chemical management decisions, and protect public health.

Evaluation of a four-zone indoor exposure model for predicting TCPP concentrations in a low-energy test house.

Numerous chemicals have been detected in indoor environments that have potential impacts on occupant health and comfort. However, due to limited resources, it's infeasible to assess indoor exposure of each chemical for all indoor conditions through measurements alone. Hence, indoor exposure models have been developed to predict time-varied exposure for a wide range of sources and chemicals under different conditions. The Indoor Environmental Concentrations in Buildings with Conditioned and Unconditioned Zones (IECCU) model was developed by the United States Environmental Protection Agency. This study evaluated the predictive ability of the IECCU by comparing airborne tris(1-chloro-2-propyl) phosphate (TCPP) concentrations measured from 2013 to 2018 in a test house to modeled predictions. Inputs to IECCU included building and environment (i.e., air zone configuration and geometry, interzonal airflow rates and air temperature in each zone), parameters for both source (spray polyurethane foam (SPF)) and sinks (gypsum and wallboard), and simulation conditions. Simulations were conducted using three sets of inputs. Simulation 1 and 2 differed in using quantified versus design inputs for temperatures and airflow rates. Simulation 1 and 3 differed in the configured air zones in the IECCU model. Given the best available inputs (Simulation 1), IECCU predicted basement concentrations that were generally higher but within a factor of three of the measurements. The basement prediction/measurement ratios for all three simulations ranged from 0.5 to 8.3 and the average was 2.9, while the predicted concentrations in the living zone were generally lower but still within an order of magnitude of the measurements. The prediction accuracy decreased with time. For Simulation 1, predicted basement concentrations were on average 1.4 times higher than measurements in 2013 and 2014. However, the ratio increased to 4.7 in 2018. The design inputs of Simulation 2 resulted in greater discrepancy between measurements and predictions than the measured inputs of Simulation 1. In addition, Simulation 2 did not capture diurnal variation as well as Simulation 1. Comparisons of Simulation 1 and 2 demonstrate the importance of using accurate temperature and airflow model inputs for more accurately predicting concentrations. Furthermore, a sensitivity analysis indicated that to improve the accuracy of IECCU predictions for TCPP emission from SPF, efforts are needed to accurately measure the mass transfer parameters for SPF, especially the SPF/air partition coefficient and the initial TCPP concentration in SPF.

Measurement of chemical emission rates from cigarette butts into air.

This study examined airborne emissions from cigarette butts for styrene, 2-methyl-2-cyclopenten-1-one, naphthalene, triacetin, and nicotine. Ten experiments were conducted by placing butts in a stainless steel chamber and measuring the chemical concentrations in chamber air. Emission rates were determined from the concentrations. Triacetin and nicotine concentrations were roughly 50% of initial concentrations after 100 hours, while concentrations of other chemicals decayed to less than 10% of initial concentrations within 24 hours. Initial emission rates per cigarette butt ranged from 200 to 3500 ng h-1 . Triacetin and nicotine emission rates at 25°C were 1.6 to 2.2 times higher than the rates at 20°C, while the emission rates of other chemicals at 25°C were 1.1 to 1.3 times higher than the rates at 20°C only during the first sampling period. The chemical concentrations and emission rates at 30°C were comparable or lower than the values at 25°C, possibly due to different batches of cigarettes used. The 24-hours emitted mass of nicotine from a cigarette butt at 25°C could be up to 14% of the literature reported nicotine masses emitted from a burning cigarette.

Applicability of Spray Polyurethane Foam Ventilation Guideline for Do-It-Yourself Application Events.

Small two-component spray polyurethane foam (SPF) application kits are often applied by Do-It-Yourself (DIY) consumers. The United States Environmental Protection Agency (EPA) publishes a guideline for ventilating a space where SPF is being applied to minimize exposure to mists, vapors, particles and dust. This study sought to assess the applicability of the EPA ventilation guideline in protecting non-application areas of a house from exposure to SPF-associated emissions during a DIY application. Specifically, the research sought to determine if the flame retardant in SPF, Tris(1-chloro-2-propyl)-phosphate (TCPP), migrates outside a temporarily-constructed isolation area during and after a SPF application in the basement of a test home. Tracer decay tests were used to characterize the enhanced ventilation during application. The tracer gas results highlighted the importance of setting up the house internal and external openings to achieve effective isolation and ventilation of the spray area. The DIY spray led to a statistically significant increase in the airborne TCPP concentration in the basement during the first eight hours after application. However, the basement TCPP concentrations during and immediately after the SPF application were not statistically different from the TCPP concentrations in the basement (associated with the application of SPF during construction) measured four years prior to this application. The data indicate that, for the case tested in this study, following the EPA SPF ventilation guideline protected the rest of the house from elevated TCPP concentrations. However, these results may not hold for higher loading rates, lower airflow rates, leakier isolation enclosures or non-analyzed chemicals.

Ultrafine particle removal and ozone generation by in-duct electrostatic precipitators.

Human exposure to airborne ultrafine particles (UFP, < 100 nm) has been shown to have adverse health effects and can be elevated in buildings. In-duct electrostatic precipitator filters (ESP) have been shown to be an effective particulate control device for reducing UFP concentrations (20-100 nm) in buildings, although they have the potential to increase indoor ozone concentrations. This study investigated residential ESP filters to reduce ultrafine particles between 4 to 15 nm and quantified the resulting ozone generation. In-duct ESPs were operated in the central air handling unit of a test house. Results for the two tested ESP brands indicate that removal efficiency of 8 to 14 nm particles was near zero and always less than 10% (± 15%), possibly due to particle generation or low charging efficiency. Adding a media filter downstream of the ESP increased the decay rate for particles in the same size range. Continuous operation of one brand of ESP raised indoor ozone concentrations to 77 ppbv and 20 ppbv for a second brand. Using commercial filters containing activated carbon downstream of the installed ESP reduced the indoor steady-state ozone concentrations between 6% and 39%.

Ozone generation and chemistry from 222 nm germicidal ultraviolet light in a fragrant restroom.

Devices using 222 nm germicidal ultraviolet light (GUV222) have been marketed to reduce virus transmission indoors with low risk of occupant harm from direct UV exposure. GUV222 generates ozone, an indoor air pollutant and oxidant, under constrained laboratory conditions, but the chemistry byproducts of GUV222-generated ozone in real indoor spaces is uncharacterized. We deployed GUV222 in a public restroom, with an air change rate of 1 h-1 one weekend and 2 h-1 the next, to measure ozone formation and byproducts generated from ozone chemistry indoors. Ozone from GUV222 increased background concentrations by 5 ppb on average for both weekends and reacted rapidly (e.g., at rates of 3.7 h-1 for the first weekend and 2.0 h-1 for the second) with gas-phase precursors emitted by urinal screens and on surfaces. These ozone reactions generated volatile organic compound and aerosol byproducts (e.g., up to 2.6 µg m-3 of aerosol mass). We find that GUV222 is enhancing indoor chemistry by at least a factor of two for this restroom. The extent of this enhanced chemistry will likely be different for different indoor spaces and is dependent upon ventilation rates, species and concentrations of precursor VOCs, and surface reactivity. Informed by our measurements of ozone reactivity and background aerosol concentrations, we present a framework for predicting aerosol byproduct formation from GUV222 that can be extended to other indoor spaces. Further research is needed to understand how typical uses of GUV222 could impact air quality in chemically diverse indoor spaces and generate indoor air chemistry byproducts that can affect human health.

The chemical assessment of surfaces and air (CASA) study: using chemical and physical perturbations in a test house to investigate indoor processes.

The Chemical Assessment of Surfaces and Air (CASA) study aimed to understand how chemicals transform in the indoor environment using perturbations (e.g., cooking, cleaning) or additions of indoor and outdoor pollutants in a well-controlled test house. Chemical additions ranged from individual compounds (e.g., gaseous ammonia or ozone) to more complex mixtures (e.g., a wildfire smoke proxy and a commercial pesticide). Physical perturbations included varying temperature, ventilation rates, and relative humidity. The objectives for CASA included understanding (i) how outdoor air pollution impacts indoor air chemistry, (ii) how wildfire smoke transports and transforms indoors, (iii) how gases and particles interact with building surfaces, and (iv) how indoor environmental conditions impact indoor chemistry. Further, the combined measurements under unperturbed and experimental conditions enable investigation of mitigation strategies following outdoor and indoor air pollution events. A comprehensive suite of instruments measured different chemical components in the gas, particle, and surface phases throughout the study. We provide an overview of the test house, instrumentation, experimental design, and initial observations - including the role of humidity in controlling the air concentrations of many semi-volatile organic compounds, the potential for ozone to generate indoor nitrogen pentoxide (N2O5), the differences in microbial composition between the test house and other occupied buildings, and the complexity of deposited particles and gases on different indoor surfaces.

Ozone Generation from a Germicidal Ultraviolet Lamp with Peak Emission at 222 nm.

Recent interest in commercial devices containing germicidal ultraviolet lamps with a peak emission wavelength at 222 nm (GUV222) has focused on mitigating virus transmission indoors while posing minimum risk to human tissue. However, 222 nm light can produce ozone (O3) in air. O3 is an undesirable component of indoor air because of health impacts from acute to chronic exposure and its ability to degrade indoor air quality through oxidation chemistry. In seven four-hour experiments we measured O3 produced from a single filtered GUV222 lamp in a 31.5 m3 stainless steel chamber. Using an emission model, we determined an O3 generation rate of 19.4 ppbv h-1 ± 0.3 ppbv h-1 (equivalent to 1.22 mg h-1 ± 0.02 mg h-1). We estimated the fluence rate from the lamp using two methods: (1) chemical actinometry using tetrachloroethylene (actinometry) and (2) geometric projection of the irradiance field from radial and angular distribution measurements of the GUV222 lamp fluence (irradiance). Using the estimated lamp fluence rates of 2.2 µW cm-2 (actinometry) and 3.2 µW cm-2 (irradiance) we predicted O3 production in our chamber within 20 % of the average measured mixing ratio. Future studies should evaluate the indoor air quality impacts of GUV222 technologies.

The persistence of smoke VOCs indoors: Partitioning, surface cleaning, and air cleaning in a smoke-contaminated house.

Wildfires are increasing in frequency, raising concerns that smoke can permeate indoor environments and expose people to chemical air contaminants. To study smoke transformations in indoor environments and evaluate mitigation strategies, we added smoke to a test house. Many volatile organic compounds (VOCs) persisted days following the smoke injection, providing a longer-term exposure pathway for humans. Two time scales control smoke VOC partitioning: a faster one (1.0 to 5.2 hours) that describes the time to reach equilibrium between adsorption and desorption processes and a slower one (4.8 to 21.2 hours) that describes the time for indoor ventilation to overtake adsorption-desorption equilibria in controlling the air concentration. These rates imply that vapor pressure controls partitioning behavior and that house ventilation plays a minor role in removing smoke VOCs. However, surface cleaning activities (vacuuming, mopping, and dusting) physically removed surface reservoirs and thus reduced indoor smoke VOC concentrations more effectively than portable air cleaners and more persistently than window opening.

Influence of temperature, relative humidity, and water saturation on airborne emissions from cigarette butts.

With five trillion generated per year, cigarette butts are some of the most common litter worldwide. However, despite the potential environmental and human health risks from cigarette butts, little effort has been made to understand airborne emissions from cigarette butts. This study examined the influence of temperature, relative humidity and water saturation on airborne chemical emissions from cigarette butts. Experiments were conducted to measure the emitted chemical masses from butts using headspace analysis after the butts were conditioned in a controlled chamber under four conditions (30 °C and 25% relative humidity (RH), 30 °C and 50% RH, 40 °C and 25% RH, 40 °C and 50% RH) and in an outdoor environment (two sets of experiments in both summer and winter). The measured target chemicals included furfural, styrene, ethylbenzene, 2-methyl-2-cyclopenten-1-one, limonene, naphthalene, triacetin, and nicotine. Results indicate that increased temperature increased the emission rates of all target chemicals from the butts conditioned in both chambers and outdoors. In addition, water has considerable influence on the emission rates from the butts. Seven of the eight chemicals were emitted faster from butts at 50% RH compared to 25% RH. During water saturation, chemicals with high water solubility and partition coefficient between water and air, e.g., triacetin and nicotine, mainly migrate into the surrounding environment via aqueous rather than airborne routes. This highlights the importance of rainfall events on airborne emission variability for triacetin and nicotine. Water saturation increased the decay rate (decreased the decay time) of emitted mass measured in headspace analysis for the two carbonyl chemicals: furfural and 2-methyl-2-cyclopenten-1-one, while it decreased the decay rate (increased the decay time) for the three hydrocarbons (styrene, limonene, and naphthalene).

Evaluating IAQ and Energy Impacts of Ventilation in a Net-Zero Energy House Using a Coupled Model.

The National Institute of Standards and Technology constructed the Net-Zero Energy (NZE) Residential Test Facility to support the development and adoption of cost-effective NZE designs and technologies. In support of indoor air quality goals, contaminant source control approaches were implemented that minimized the use of products containing urea-formaldehyde resin and utilized products with relatively low volatile organic compound emissions. Indoor and outdoor concentrations of formaldehyde and acetaldehyde were measured approximately monthly for 15 months. Independent emission measurements of formaldehyde were made in a small chamber system to determine the emission rates from samples of the wood flooring, plywood, and wood cabinetry taken from the house. Blower door tests were performed to determine the leakage area of the exterior envelope, the interior floors, and transfer grilles between floors. Real-time formaldehyde concentration and energy measurements were used to verify the indoor concentrations and energy predictions of a coupled CONTAM-EnergyPlus model of the house. The verified model was then used to evaluate the impacts of different outdoor air ventilation rates on indoor concentrations and energy. This work demonstrates the need for consideration of source control options during product selection and the provision of mechanical ventilation, especially in homes with relatively airtight envelopes.

Methyl bromide as a building disinfectant: interaction with indoor materials and resulting byproduct formation.

Several buildings were contaminated with Bacillus anthracis in the fall of 2001. These events required consideration of how to disinfect large indoor spaces for continued worker occupation. The interactions of gaseous disinfectants with indoor materials may inhibit the disinfection process, cause persistence of the disinfectant, and lead to possible byproduct formation and persistence. Methyl bromide (CH3Br) is a candidate for disinfection/deactivation of biological agents in buildings. In this study, 24 indoor materials were exposed to CH3Br for 16 hr at concentrations ranging from 100 to 2500 ppm in 48-L electropolished stainless steel chambers. CH3Br concentrations were measured during and after disinfection. Its interactions with materials were observed to be small, with nearly complete and rapid desorption. Between 3% and 8% of CH3Br adsorbed to four materials (office partition, ceiling tile, particle-board, and gypsum wallboard with satin paint), and the degree of adsorption decreased with increasing relative humidity. The percentage of adsorption to all other materials was <2%. This result suggests that when designing disinfection events with CH3Br, loss to indoor materials can be neglected in terms of disinfectant dose calculations. Possible reaction products were identified and/or quantified before and after exposure to CH3Br. Several monomethylated and dimethylated aliphatic compounds were observed in chamber air at low concentrations after the exposures of six materials to CH3Br. Concentration increases also occurred for chemicals that were observed to naturally off-gas from materials before exposure to CH3Br, suggesting that CH3Br may play a role in enhancing the natural off-gassing of chemicals, for example, by competitive displacement of compounds that already existed in the materials. The results described in this paper should facilitate the design of building disinfection systems involving CH3Br.

Workgroup report: Indoor chemistry and health.

Chemicals present in indoor air can react with one another, either in the gas phase or on surfaces, altering the concentrations of both reactants and products. Such chemistry is often the major source of free radicals and other short-lived reactive species in indoor environments. To what extent do the products of indoor chemistry affect human health? To address this question, the National Institute for Occupational Safety and Health sponsored a workshop titled "Indoor Chemistry and Health" on 12-15 July 2004 at the University of California-Santa Cruz. Approximately 70 experts from eight countries participated. Objectives included enhancing communications between researchers in indoor chemistry and health professionals, as well as defining a list of priority research needs related to the topic of the workshop. The ultimate challenges in this emerging field are defining exposures to the products of indoor chemistry and developing an understanding of the links between these exposures and various health outcomes. The workshop was a step toward meeting these challenges. This summary presents the issues discussed at the workshop and the priority research needs identified by the attendees.

Measuring and Characterizing Tris(2-chloro-1-methylethyl) Phosphate Emission from Open Cell Spray Polyurethane Foam.

Understanding emission of Tris(2-chloro-1-methylethyl) Phosphate (TCPP) from spray polyurethane foam (SPF) insulation will contribute to the assessment of exposure to TCPP in indoor environments. This study aims to: (1) develop a method to determine the gas phase concentration of TCPP in equilibrium with the material phase (y0) for open cell SPF, (2) determine the partition coefficient for TCPP between air and SPF (K), and (3) examine the influence of temperature on y0 and K. The emission of TCPP from two kinds of open cell SPF in a closed micro-chamber without flow are being tested. The steady-state gas phase TCPP concentration in the chamber (C equ) is also being measured. Cm 0 (the initial concentration of TCPP in SPF) is measured using a solvent extraction method. C equ and C m0 will then be used to determine y0. These measurements are still in progress, and the preliminary results will be presented at the conference.

Formaldehyde Concentrations in a Net-Zero Energy House: Real-time Monitoring and Simulation.

Measured real-time formaldehyde concentrations in a net-zero energy house were compared to simulated concentrations from a recently-developed, coupled building energy and airflow/indoor air quality model. Measured and simulated formaldehyde concentrations in living spaces ranged from 4 ppbv to 10 ppbv (5 µg/m3 to 12 µg/m3) while concentrations in the conditioned attic ranged from 13 ppbv to 28 ppbv (16 µg/m3 to 34 µg/m3). During the 15 minutes the heat recovery ventilator was off each hour, the measured concentration in a bedroom increased by 1 ppbv (1.2 µg/m3). In addition, year-long simulations suggest the formaldehyde concentration in the attic may reach almost 50 ppbv (62 µg/m3) during the summer. These results highlight the need for source control and effective ventilation (both outdoor air and air distribution) to reduce the concentration of indoor pollutants, particularly in tighter buildings. This research reaffirms the need to consider buildings as multizone systems and provide adequate ventilation to all building zones, particularly those with low outdoor air change rates.

A protocol to estimate the release of anthropogenic hydrocarbons from contaminated soils.

An operational protocol, appropriate for a tier 1 or tier 2 type relative risk evaluation of a site that has polycyclic aromatic hydrocarbon (PAH) or petroleum hydrocarbon impacted soils, was developed to estimate the fraction of anthropogenic hydrophobic hydrocarbons that will be released rapidly from such soils. The development of this protocol used over 400 datasets from 40 different field samples to establish and verify the operational protocol. The datasets resulted from four-month kinetic desorption studies of these field samples. Based on the chemicals evaluated, the protocol has greatest application to two, three, and four ring-PAH and to diesel range aliphatic hydrocarbons. The protocol is a simple batch desorption analysis that uses established methods and is conducted for 7 d. The protocol results were verified with specific correlation relationships (r2 = 0.81 to 0.96) to estimate the rapidly releasing fraction (F value) that is obtained in a full, four-month chemical release evaluation.